An arms race

The P. falciparum genome contains a large family of 60 var genes that encode hypervariable P. falciparum erythrocyte membrane protein 1 (PfEMP1). During the erythrocytic stage, each parasite expresses one of its var genes at a time. By switching between different var genes during the course of infection, the parasite is able to evade destruction by host immunity. P. vivax can only enter erythrocytes with genetically determined receptor sites known as Duffy blood groups. Sickle cell anaemia is protective against malaria; heterozygotes have some normal haemoglobin and have 80-95% protection against P. vivax.